In the manufacture of low density ethylene polymers by a continuous mass polymerization process the ethylene is polymerized to a conversion of less than 20% at a temperature in excess of 200.degree. C. and at a pressure in excess of 1,000 atmospheres. The product from the reactor is let down to pressures just slightly in excess of atmospheric pressure in one or more pressure let-down vessels to remove substantially all unpolymerized ethylene from the ethylene polymer. The molten ethylene polymer then is extruded, cooled with water, and cut into pellets. The pellets then are dried and transferred to suitable bins for storage.
The pelletized ethylene polymer contains small quantities of ethylene gas which may amount to about 0.1 weight % of the polymer. This gas diffuses into the water used to cool the pellets and into the atmosphere in the dryer and storage bins. The concentration of the ethylene gas in the air is so low that it is not economically feasible to collect and recycle it, or to burn it in catalytic converters. While the concentration of ethylene gas is too low for economic recovery or burning by existing techniques, the total quantity of ethylene gas presently lost to the atmosphere in a large polymer production plant can easily exceed 1.000 lbs./day. The loss of this ethylene to the atmosphere is objectionable from a view of air quality.
In view of the above facts, there is a need in the art for an efficient and low cost process for recovering and/or burning the dilute ethylene gas presently lost to the atmosphere in ethylene polymer production facilities.